Vehicles with parallel hybrid powertrains known from practical applications are typically constructed (between an internal combustion engine and the output of the vehicle) with a starting element, configured as a frictionally engaged clutch, in order to start the vehicle in the conventional manner using the internal combustion engine. The starting element during the starting process is initially operated with slip. When a vehicle of this type is additionally provided with a drive assembly configured as an electric motor, the controlled and regulated slip operation of the starting element is not required when starting the vehicle by using only the electric motor since electric motors, unlike conventional internal combustion engines, have no minimum rotational speed.
A method for controlling and regulating a powertrain of a hybrid vehicle and a powertrain of a hybrid vehicle having a frictional engagement starting clutch is known from DE 10 2004 002 061 A1. Using the method, according to the invention, for controlling and regulating a powertrain of a hybrid vehicle comprising an internal combustion engine, an electric motor, a shifting element disposed between the electric motor and an output in a power flow of the powertrain and designed with continuously variable transmission capacity, as well as a clutch device disposed between the electric motor and the internal combustion engine, via which clutch device the electric motor and the internal combustion engine can be operatively connected with each other, a powertrain of a hybrid vehicle can be operated such that a transition can be effected from driving the hybrid vehicle via the electric motor to a parallel operation of the hybrid vehicle via the electric motor and the internal combustion engine, or to only driving the hybrid vehicle via the internal combustion engine, as well as that a starting operation can be achieved of the internal combustion engine via the electric motor, without any reaction torque of the powertrain being noticeable to the driver of the hybrid vehicle.
For this purpose, during operation of the powertrain, the transmission capacity of the shifting element is adjusted during a starting phase of the internal combustion engine such that, at the output of the powertrain, the torque that is applied is independent from a starting phase of the internal combustion engine, wherein torque changes at the output, which occur due to the starting phase of the internal combustion engine, are preferably prevented by a slip operation of the shifting element.
With this method, during the starting phase of the internal combustion engine, the rotational speed of the electric motor is raised to a speed value at which it is guaranteed that the shifting element between the electric motor and the output of the powertrain is held in a slip operation during the entire starting phase of the internal combustion engine. The rotational speed value is computed by an algorithm implemented in the engine control and/or in the transmission control and/or in a higher-ranking torque manager.
In addition, powertrains of vehicles comprising internal combustion engines having minimum rotational speeds are known from practice, which for the implementation of a starting process of the vehicle via the internal combustion engine are provided with a hydrodynamic torque converter and a corresponding converter lock-up clutch, wherein the torque converter and the converter lock-up clutch are controlled and regulated in the conventional manner as a function of the operational state of the powertrain of the vehicle.
It is, therefore, the object of the invention to provide a method for operating a parallel hybrid powertrain of a vehicle. The powertrain having a starting element configured with a hydrodynamic torque converter and a corresponding converter lock-up clutch, the use of which element minimizes the influence of the torque converter on a target output torque to be applied on the output during a starting phase of the internal combustion engine via the electric motor.